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Possible fix for ATX low voltage shutdown

Posted by kratz9 
Possible fix for ATX low voltage shutdown
March 31, 2013 12:15AM
I'm not sure if this method has been posted here before so I thought I would share.

I, like many it seems, was struggling with my ATX power supply shutting down during prints. Even with a 2.5 amp load on the 5V rail. Looking around I stumbled on this page,


This person was using the ATX to drive an audio amplifier, which would often trip the over-current protection on the supply. They were able to disable the over-current protection by disconnecting a pin on the control IC. That's probably a bad Idea in general, but at the end of that page it referenced a second type of control IC, which also provides under-voltage protection.

From what I've read on the forums here from others, the supply shutting down, when not because of a short, is likely because of the under-voltage protection kicking in. This has something to do with the way the voltage is regulated, when all the current is being pulled off just the 12v side, the voltage will drop slightly on the 12v, and more so on the smaller voltage rails. The large drop on the small side is what trips the protection. This is where the loading of the 5v and sometimes 3.3v rail comes up (to balance the regulator out and reduce the voltage drop). The page also revealed that not all power supplies use the under-voltage protection, which would make sense since many on the forums here say they have no problem running ATX supplies without loading the 5V rail.

Back to the ATX control IC, the second control chip listed on that page was the EST7502B, which allows you to disable under-voltage protection by grounding pin #4, and upon opening my supply I had the same, labeled EST. 7502C. That page linked to another page, which linked to a data sheet for the EST7502, which showed that pin #5 was ground, so it seemed like this would be pretty easy.

This page has the link to the datasheet, as well as a bunch of other control chips that are used. http://www.hardwaresecrets.com/article/Everything-You-Need-to-Know-About-Power-Supply-Protections/905/7

So, I did that, took apart the power supply, cut the trace on the PCB to pin #4, and soldered a jumper to the adjacent ground pin #5. In theory this has disabled the under-voltage protection. A little bit of testing shows that the supply at least still turns on and seems to run without shutting itself off now, of course time may tell if that is truly the case.

I've attached a picture of the IC in my supply, the trace cut and jumper on the PCB. For reference, this is the supply I was using, http://www.newegg.com/Product/Product.aspx?Item=N82E16817170010

And feel free to correct me if I'm wrong about any of this, just piecing together info from here and there.
open | download - ATX-EST7502 front.png (270.1 KB)
open | download - ATX-EST7502 back.png (378.5 KB)
Re: Possible fix for ATX low voltage shutdown
March 31, 2013 12:36AM
Never mind, I should have know, almost as soon as I posted this it shut itself off again.
Edit, I think I'm going to try disabling the over-voltage protection by grounding pin three. If that doesn't work, I'll disable the 3.3v and 5v ovp by grounding pins #1, and #2 as well. I'm determined to make this work, and I'm still fairly sure I don't have a short.

Edit 2: so far so good with disconnecting and grounding pin #3, been messing with my printer for a couple hours now without a shutdown. This might be a winner.

Edited 2 time(s). Last edit at 03/31/2013 04:25PM by kratz9.
Re: Possible fix for ATX low voltage shutdown
March 31, 2013 06:13PM
Nevermind again, I keep posting prematurely. Darn thing still shuts off for no reason.

Edit: as a last resort, I've grounded pins 1,2,3, and 4. Now there should be no voltage monitoring active to shut down the supply. As a test, like in article I linked to, I tapped the 12v and ground wires together momentarily, and the supply no longer shuts off like it usually would. I'll give this a go on some printing, and hopefully, this time, it will allow me to print uninterrupted.

Edited 2 time(s). Last edit at 03/31/2013 07:02PM by kratz9.
Just wondering if you had any success since your last update? Thanks for the info you have provided thus far.
Re: Possible fix for ATX low voltage shutdown
May 20, 2013 09:18PM
I had my one ATX power supply continuously shut itself down.

I grabbed a buddies of mine, and so far it works without shutting down.
Re: Possible fix for ATX low voltage shutdown
May 20, 2013 10:17PM
Yeah, since the last fix I made to the supply its worked wonderfully. No unexpected shutdowns since.
Re: Possible fix for ATX low voltage shutdown
December 24, 2014 03:08AM
All of you guys are a real help to me by posting about ATX power supplies. It seems that the 550 watt logisys is the power supply of choice since it is relatively cheap and easy to mod.
I guess i'll try the shorting of the pins on the EST 7502C and cross my fingers.

BTW , do the other pins have to have the traces cut as well?

Edited 1 time(s). Last edit at 12/24/2014 03:10AM by iceburgh.
Re: Possible fix for ATX low voltage shutdown
December 24, 2014 06:00PM

Well it worked!

Now have the same results as Kratz9.

Power supply doesnt shut off anymore.
Re: Possible fix for ATX low voltage shutdown
January 01, 2015 10:07AM
Anyone ever tackled the variable voltage mod on the 550 watt logisys power supply?
Re: Possible fix for ATX low voltage shutdown
January 01, 2015 02:04PM
Those ATX power supplies are switchers designed to power electronic loads not inductive loads like motors. When you decelerate a couple of axis at the same time the motors act as generators and push the power back.to the power supply driving the voltage way up. This why they trip. My linear power supply with a large transformer, hefty diode bridge, and big filter caps absorbs that voltage surge easily and uses it to drive the motors.
Re: Possible fix for ATX low voltage shutdown
January 17, 2015 06:11PM
Hey, I have the same PSU and I wasn't even able to turn it on... Almost buy another but tried your mod and it works great!
The voltages are a bit high though (12v > 13,5v, 5v > 6v), there would be any problem?
Thank you very much for your post!
Re: Possible fix for ATX low voltage shutdown
January 17, 2015 06:22PM
Cool, glad it helped. It shouldn't be an issue. It depends on your electronics, but I'd hope max voltage on the regulators, FETs, and motor drivers should be well above 12V anyways. Probably a bad idea to use it for a computer anymore, but good enough for a printer.
Re: Possible fix for ATX low voltage shutdown
October 06, 2015 07:26AM
Sorry, but iam having this power supplies with the same problems, but having no much knoledge on power supplies.
they dont have the same ICs as that you have mentioned, and they have two ICs, one is for the voltage protection, how can i disable this volatage protection.
the power supply just shut down after a short start, and take a time to start again.
open | download - circuit1.jpg (151.9 KB)
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